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Planet hiding in the Inner Oort Cloud

"There is a theory that is being tested that there could be a planet orbiting the Sun at a distance that would match the distance that the Inner Oort Cloud is. The planet is about 10 times the mass of the Earth and would orbit the Sun every 15,000 years.

The planet is only a theory at the moment. Neptune was first theorized and its position was calculated before it was actually discovered so there's no reason why the same can't hold true for this new planet.

The evidence for the new planet is based on the orbits of other far out objects such as Sedna. All the far off objects are all orbiting in the same direction as the diagram demonstrates, the reason for that is believed to be a massive object in the other direction. Ref: Space."

The questions are as follow:

If we see Sedna and all the other objects, why we can't see that hiding Planet?
Could it be that there is no planet there?
Could it be that those objects are just orbit around their virtual barycenter?

If we see Sedna and all the other objects, why we can't see that hiding Planet?

Sedna is currently less than 100AU from the Sun (although its aphelion is around 1000AU). The proposed planet is around 700AU away. A combination of a very large area to search and a very dim target makes for a difficult project.

Originally Posted by Dave Lee

Could it be that there is no planet there?

Yup, the evidence is not yet conclusive. If this is based on the paper that was discussed on here a while back the calculations were partially analytic and partially numeric, using a central mass with additional perturbative terms and then using random distributions of smaller bodies as part of an n-body simulation to model the evolution of the system. There was scope for the alignments to be a result of perturbations from TNOs/Scattered disk objects if the distribution used was a poor fit to the actual distribution. There may be a follow up where they address that though.

Sedna is currently less than 100AU from the Sun (although its aphelion is around 1000AU). The proposed planet is around 700AU away. A combination of a very large area to search and a very dim target makes for a difficult project.

Yes, that is correct if we only focus on Sedna.

However, there are several objects/moons in an orbital cycle around that hidden planet.
Please look again at the diagram:

We can see clearly that the estimated aria for that planet is very limited.
Its mass is quite high: "The planet is about 10 times the mass of the Earth and would orbit the Sun every 20,000 years".
Therefore, if we can see and monitor all of those relativity small objects/moons as sedna how can we miss that big planet which its potential location is quite clear to us?

In the following article it is stated:https://arxiv.org/pdf/1601.05438.pdf
"Here, we have proposed that the process of resonant coupling with a distant, planetary mass companion can explain the available data, and have outlined an observational test that can validate or refute our hypothesis."

However, if we still can't find that hidden planet (and assuming that we won't find it in the future), than could it be that we have to refute our hypothesis?

Therefore, if we can see and monitor all of those relativity small objects/moons as sedna how can we miss that big planet which its potential location is quite clear to us?

Because its location isn't clear. There are a lot of orbits that fit the parameters. And 10 Me is not that large. And 700 AU is 7x further away than Sedna or the other scattered disk objects.

Remember the dimmer the target (and targets dim with range) the smaller the field of view you can generally collect and search. The further out the target the smaller the angular rate of change is you have to search for. It is simply a hard search to do. Remember Pluto took 30 years to find, Neptune took 6. And those were much easier and better constrained searches. Yes, technology has moved on and there is far more automation in play. But it is still not easy to find things even when you know a few orbital parameters for them.

Originally Posted by Dave Lee

In the following article it is stated:https://arxiv.org/pdf/1601.05438.pdf
"Here, we have proposed that the process of resonant coupling with a distant, planetary mass companion can explain the available data, and have outlined an observational test that can validate or refute our hypothesis."

However, if we can't find that hidden planet (and assuming that we won't find it in the future), than could it be that we have to refute our hypothesis?

They would have to refute their hypothesis if it failed observational tests, yes. But since finding their target planet is so hard they have considerable wiggle room left. Of course the corollary is that until they have that evidence their hypothesis remains unproven.

However, there are several objects/moons in an orbital cycle around that hidden planet.
Please look again at the diagram:

Those bodies we do see are orbiting the Sun, not the reputed planet which would have about 1/30,000 of the Sun's mass. The theory is that perturbations by that planet over a period of billions of years have tweaked those orbits into the observed clustering of the orientations of the ellipses.

We can see clearly that the estimated aria for that planet is very limited.

I can clearly see someone's estimate of a possible orbit of that planet, but the creators of that web page did not give us the amount of uncertainty.

Those bodies we do see are orbiting the Sun, not the reputed planet which would have about 1/30,000 of the Sun's mass. The theory is that perturbations by that planet over a period of billions of years have tweaked those orbits into the observed clustering of the orientations of the ellipses.

Good catch, I had not noticed that misconception. Dave, you have misinterpreted the diagram. No one is suggesting that the scattered disk objects orbit the hypothetical planet. They orbit the Sun, as Hornblower says.

So, the bright point in the diagram doesn't represent the hidden planet.
It just gives an indication for the estimated point of the orbitals braycenter.
The hidden planet can hide anywhere.
However, its gravity effects the location of that estimated brycenter.
Therefore, just after finding that hidden planet we can try to calculate if our hypothesis is valid.

So, the bright point in the diagram doesn't represent the hidden planet.

Correct, if you mean the yellow point to the right of the diagram.

Originally Posted by Dave Lee

It just gives an indication for the estimated point of the orbitals braycenter.

No, it is just a point somewhere on the most likely approximate orbit path (the orange line). It may represent the estimated position of the planet, but I can't find a source (beyond interviews with one of the scientists involved) that backs this up. The barycentre of the hypothetical planet's orbit is the really bright point in the centre of the diagram (the Sun)

Originally Posted by Dave Lee

The hidden planet can hide anywhere.

Not quite anywhere, it has to be in a subset of possible orbits to produce the perturbations. But still a large area.

Originally Posted by Dave Lee

However, its gravity effects the location of that estimated brycenter.

No, it has practically no effect on the barycentre. Orbits have more to them than just barycentres. In this case it is the argument of perihelion that they are looking at. This is the angle between the point of perihelion and the ascending node.

Originally Posted by Dave Lee

Therefore, just after finding that hidden planet we can try to calculate if our hypothesis is valid.

Yup - if they find it and its parameters match the predictions closely then the hypothesis was good.

Let me point out that the six observed dwarf planets are all near perihelion in elongated orbits in which they will spend most of their time near aphelion. There could easily be 10 times their number in similar orbits but currently in the outer reaches of those orbits where they would be even more elusive than the reputed Planet 9. If we could somehow see them and find that the ellipses are similarly clustered toward the left, that would reinforce the theory of Planet 9 and firm up the estimate of its orbit and position.

Let me point out that the six observed dwarf planets are all near perihelion in elongated orbits in which they will spend most of their time near aphelion..

How can we explain the observation that those six dwarf planets are all near perihelion?
Are they moving as a group?

They are orbiting the Sun at a quite long orbital radius (100AU - 1000AU).
So, could it be that at that distance the local gravity force between them is stronger than the direct gravity force between the Sun and each one of them?
Therefore, do you see any feasibility for gravity bonding between those planets, while all of them orbit as a group around the Sun?

How can we explain the observation that those six dwarf planets are all near perihelion?
Are they moving as a group?

They are orbiting the Sun at a quite long orbital radius (100AU - 1000AU). So, could it be that at that distance the local gravity force between them is stronger than the direct gravity force between the Sun and each one of them?
Therefore, do you see any feasibility for gravity bonding between those planets, while all of them orbit as a group around the Sun?

My bold. No way. They are about as far from each other as they are from the Sun, and have far less than a millionth of a solar mass apiece.

Originally Posted by ronin

Because that's when they are most likely to be detected, there are very likely many times that number which have yet to be found simply because they are currently too distant and faint to be observed.

In addition to that, their motion will be slower out there, and thus less attention-catching.